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But what, if anything, came before the prevailing cosmological explanation for the universe?

Zilch, according to Stephen Hawking.

“Nothing was around before the big, big bang,” the famed physicist told Neil deGrasse Tyson during an interview for Tyson’s “Star Talk” radio show (video below).

It’s a lot more complicated than that, though.

“According to Einstein’s General Theory of Relativity, space and time together form a space-time continuum,” Hawking said, “which is not flat, but curved by the matter and energy in it.”

He illustrates this using a Euclidean approach to quantum gravity, in which ordinary real time is replaced by imaginary time that behaves like a fourth direction of space.

“In the Euclidean approach, the history of the universe in imaginary time is a four-dimensional curved surface like the surface of the Earth, but with two more dimensions.”

So, six dimensions? Huh?

Hawking believes the universe has no outer limits; he and scientist Jim Hartle previously proposed the so-called “no-boundary condition.” That is, “the boundary condition of the universe is that it has no boundary.”

Think of it this way: The Euclidean space-time continuum is a closed surface without end—like the surface of the Earth.

“One can regard imaginary and real time as beginning at the South Pole, which is a smooth point of space-time where the normal laws of physics hold,” Hawking told Tyson. “There is nothing south of the South Pole, so there was nothing around before the big bang.”

Simple as that.

Astronomers have long searched for answers to questions like Tyson’s.

Last week, stargazers at MIT’s Haystack Observatory discovered evidence of the first light of some of the first stars. Using a radio antenna, they detected faint signals of hydrogen gas, possible only in the presence of the earliest stars—which likely began blinking on some 180 million years after the big bang.